1. Field of the Invention
The invention relates to a light water reactor with a reactor pressure vessel, a core being composed of fuel elements and being disposed in the lower half of the reactor pressure vessel, and a column of water covering the core and being used as a coolant and a moderator, the column having an initial level range during normal operation.
2. Summary of the Invention
It is accordingly an object of the invention to provide a light water reactor, in particular a boiling water reactor with a high degree of inherent safety, which overcomes the disadvantages of the heretofore-known devices of this general type and which increases the degree of inherent safety of such a boiling water reactor by the use of passively operating safety devices.
With the foregoing and other objects in view there is provided, in accordance with the invention, a light water reactor, comprising a reactor pressure vessel having an interior, a core disposed in a lower half of the pressure vessel, fuel assemblies disposed in the core, and a column of water covering the core and acting as a coolant and a moderator, the column having an initial level range during normal operation; a passively operating safety device; and fluid lines connected between the safety device and the interior of the pressure vessel, the fluid lines having means for automatically transmitting an actuation criterion to the safety device, with at least a drop of a level in the pressure vessel to a value below the initial level range serving as the actuation criterion.
In accordance with another feature of the invention, the pressure vessel has a steam space; the safety device is a switching vessel in the form of a pressure vessel with a fluid space and a gas cushion space, the switching vessel has heat exchanging pipes being submerged in the fluid space and having one end communicating with the steam space and another end communicating with the reactor water column during normal operation or when the initial level range is present; the switching vessel initiates condensation in the heat-exchanging pipes if a flow of steam occurs from the reactor interior into the heat exchanging pipes, when dropping below the initial level region of the reactor water; and including at least one of pilot and main fittings, an increase in pressure due to absorbed condensation heat in the switching vessel being used as a derived actuation criterion for passive actuation of the at least one of pilot and main fittings.
In accordance with a further feature of the invention, there are provided control rods to be inserted into the core, the at least one of pilot and main fittings actuated when the derived actuation criterion has been fulfilled, include live steam penetration fittings, the at least one of pilot and main fittings actuate a closing of the live steam penetration fittings as a safety measure and/or actuate a reactor scram as a safety measure by quickly inserting the control rods in the core.
In accordance with an added feature of the invention, there is provided a condensation chamber, and blow-off units connected to the at least one of pilot and main fittings being actuated when the derived actuation criterion has been fulfilled, the blow-off units blowing-off steam in the condensation chamber to depressurize the pressure vessel or a primary loop.
In accordance with an additional feature of the invention, there is provided a containment in which the pressure vessel is disposed; the safety device being an open flooding reservoir disposed outside the pressure vessel in the containment and having a flooding water column with a water level being geodetically higher than the reactor water column; at least one connecting line serving as a fluid line connected between the interior of the pressure vessel and the flooding water column, the at least one connecting line having a non-return fitting being held in a closed position by a reactor-side overpressure in normal operation of the reactor pressure vessel and in the initial level range of the reactor water, and the non-return fitting being opened due to pressure equalization and flooding water being added to the pressure vessel through the connecting line when reaching or dropping below another level range of the reactor water column after pressure in the pressure vessel is reduced to a value approaching that of pressure in the containment.
In accordance with yet another feature of the invention, there is provided a condensation chamber below the flooding reservoir for blowing-off excess reactor steam.
In accordance with yet a further feature of the invention, the at least one connecting line has a first line section connected to the pressure vessel, a second line section connected to the flooding reservoir and an interior, the non-return fitting is connected between the first and second line sections, and the first line section slopes down toward the non-return fitting for largely preventing a transfer of heat by convection from the reactor water to an interior of the connecting line.
In accordance with yet an added feature of the invention, the reactor core has an upper edge, and the connecting line has a lower end connected to the pressure vessel at a point above the upper edge of the reactor core.
In accordance with yet an additional feature of the invention, there is provided a water reservoir containing water; the pressure vessel having a steam space; the safety device being an emergency condenser having heat exchanging pipes being disposed in the water of the water reservoir; an inlet pipe configuration interconnecting the emergency condenser and the steam space during normal operation of the reactor, and a drainage pipe configuration interconnecting the emergency condenser and a lower region of the reactor water column at a point above the reactor core; water or condensate in the heat exchanging pipes stagnates during normal operation, but reactor steam flows through the inlet pipe configuration into the heat exchanging pipes and condenses there if the level of the reactor water drops to another level below the initial level range, so that condensate flows back into the pressure vessel through the drainage pipe configuration.
In accordance with again another feature of the invention, in this embodiment as well there is provided a condensation chamber below the water reservoir for blowing-off excess reactor steam.
In accordance with again a further feature of the invention, the inlet pipe configuration has an inlet and a connection to the heat exchanging pipes and slopes downward from the inlet to the connection, and the drainage pipe configuration has a connection to the heat exchanging pipes and an outlet end and slopes downward from the connection to the outlet end.
In accordance with again an added feature of the invention, the heat exchanging pipes have first and second pipe legs and a reversing bend and are essentially hairpin shaped with respective upward and downward slopes, the first pipe leg being connected to the inlet pipe configuration and the second pipe leg being connected to the drainage pipe configuration.
In accordance with a concomitant feature of the invention, the drainage pipe configuration has a downwardly running, hairpin shaped pipe bend located on a section in a gap between the pressure vessel and the flooding reservoir, the bend forming a circulation block during normal operation.
The advantages which can be realized with the invention lie primarily in the fact that the new light water reactor is particularly well suited for the new generation of boiling water reactors having a specific power density which is preferably reduced as compared to today's power reactors, and in which a greater passive cooling water supply is made available within the plant. The new light water reactor is preferably suited for a power or output range of up to approximately 1000 MWe, whereby essential components can be taken from the base of experience with today's power reactors having approximately twice the output. In particular, the following advantages can be realized by means of the invention:
at least one safety-relevant redundancy should be passively operated (disconnect, pressure release, isolation, after-cooling, level maintenance), PA1 the holding time in which active measures (replacement measures) must be taken, can be extended to approximately seven days, PA1 active measures can then either be in the form of the start-up of existing systems or of the simple addition to the water reservoir, such as by means of fire department connections, PA1 to temper the effects of extremely unlikely core meltdowns, at least one fall back position (such as in-vessel control of the core melt, or ex-vessel cooling of an escaped core melt) is available.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a light water reactor, in particular a boiling water reactor with a high degree of inherent safety, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.